Transportation vehicles, particularly aircraft, have only a limited capacity for carrying flushing liquid for rinsing or flushing toilets and for storing the waste water that results. For this reason, transportation vehicles often use toilet systems in which the toilet bowl is connected to a waste collection tank by a suction valve, and particularly toilet systems that are constructed as vacuum systems which aim to reduce the amount of flushing liquid that is required. Conventional vacuum toilet systems in aircraft use a flushing liquid to flush the toilet bowl, whereby the flushing liquid can be fresh water or can be in part so-called gray water, i.e., fresh water that has already been used for hand washing or the like without being contaminated with fecal waste or urine, and may be supplemented by deodorizers, disinfectants, etc. The flushing liquid is sometimes referred to as “flush water” herein for simplicity.
German Patent 42 01 986 and corresponding U.S. Pat. No. 5,317,763 (Frank et al.), issued June 1994, disclose a vacuum toilet that is essentially equipped with a trigger device, a flush water valve, and a suction valve that is arranged in a connecting conduit between the toilet bowl and the waste collection tank. After the trigger is actuated, the flushing liquid is delivered to the toilet bowl by means of control devices. Subsequently, the suction valve opens and the waste contained in the toilet bowl is flushed together with the flushing liquid into the waste collection tank.
A brochure titled “Das Zentrale Vakuum Toiletten-System für die Schiffsausrüstung” (“The Central Vacuum Toilet System for the Outfitting of Ships”) from the company sanivac Vakuumtechnik GmbH of Wedel, Germany (1997) discloses a vacuum toilet system that is used for marine vessels. This system, too, requires less flushing water than the conventional gravity flush toilet systems because of the use of vacuum technology that reduces the demand for flushing liquid to approximately 1 liter per flush. This reference also discloses that the waste pipe of the system may be a steel pipe with an inner surface coating of plastic.
German Utility Model Publication DE 92 01 684 U1 discloses a toilet arrangement in which an odor-binding agent or cleaning agent is added to the flushing liquid in the flushing circuit. This increases the effectiveness of the toilet flushing and reduces the formation of odor. This reference further suggests coating the inner surface of the toilet bowl with a layer of polytetrafluoroethylene (PTFE), to facilitate the cleansing or flushing of fecal residue from the toilet bowl.
European Patent Publications EP 0,295,508 and EP 0,363,012 disclose vacuum toilet systems that use “gray water”, at least in part, for rinsing or flushing the toilet bowl. In these cases, it is necessary that the water previously used in the wash basins be processed with a suitable filter technology in order to prevent blockage of the flush water line. Thus, in addition to the necessary controls for the flushing process, it is also necessary with such systems to provide a water treatment process.
Various attempts have been made, in applications other than aircraft, to provide waterless or flushless toilet systems, i.e. toilet systems that do not require a flushing liquid for flushing the urine and fecal waste from the toilet bowl, for example as represented by U.S. Pat. No. 3,457,567 (Criss) and U.S. Pat. No. 4,346,002 (Petzinger). These are generally composting toilet systems that use a cone or wrapper of paper or plastic for receiving, containing and encapsulating the fecal waste in the toilet bowl and then transporting the resulting encapsulated package by vacuum suction through a waste line to a holding/composting tank. The encapsulating wrapper aims to prevent direct contact of the fecal waste with the inner surfaces of the toilet bowl, which of course avoids the need of cleaning or removing the fecal waste from the inner surfaces of the toilet bowl. In other words, such systems do not have any waste-contacting surfaces in the toilet bowl or waste lines, because the waste is fully encapsulated in a wrapper.
Such systems are not well suited to applications in commercial passenger transport vehicles such as aircraft, because they are not sufficiently robust and reliable. For example, experience has shown that passengers often try to dispose of various items in addition to feces and urine in the toilets, including feminine hygiene products, bottle caps, razor blades, wrappers and packaging of various products, etc. Such items will inevitably puncture the waste-encapsulating wrapper, causing feces to directly contact, soil and adhere to the inner surfaces of the toilet bowl and waste line. Also in such systems, the wrapper-providing arrangement is highly subject to malfunction and failure, and/or requires proper operating efforts and procedures by the toilet user.
Reducing the amount of water or liquid required for flushing the toilets is of great importance, particularly on board an aircraft, because this would reduce the total gross weight of the aircraft and correspondingly increase the usable carrying capacity for passengers, cargo and fuel, reduce the fuel consumption, and/or increase the flight range. It would be highly advantageous and desirable to completely eliminate the need of flushing an aircraft vacuum toilet system with a flushing liquid. On large capacity aircraft, for example that can carry up to 500 passengers, sufficient water for flushing the toilets (fresh water or “gray water”) must be provided for each passenger to use the toilet one or more times, with further consideration of the duration of the flight. Although a number of toilet systems that require a reduced volume of flushing liquid are already known, it is still important and necessary, particularly for large capacity aircraft, to further reduce or entirely eliminate the water demand for flushing and rinsing purposes. This is particularly true for large capacity aircraft that fly long distances (i.e. long flight durations) and, accordingly, must otherwise carry an enormous amount of water. The toilet system for an aircraft must also have a high reliability, ease of use, and low maintenance requirements.